The present invention relates to an improved developing solution for positive-working photoresist compositions or, more particularly, to an improved developing solution suitable for use in patterning of a layer of a quinone diazide-based positive-working photoresist composition. The developing solution is imparted with enhanced wettability of the surface of the photoresist layer and dissolving selectivity between the exposed areas and unexposed areas improved so much that no defects are caused in the developed pattern of the photoresist layer. Further, development with the developing solution can be performed with little temperature dependency of the dissolving power in the exposed areas of the photoresist layer.
In the conventional procedures for the manufacture of semiconductor IC devices, photomasks for the manufacture of ICs, printed circuit boards and the like, the substrate plate is subjected to a selective treatment before etching, diffusion and other treatments. With an object to selectively protect certain areas of the substrate surface which should be left intact by the treatment in this case, it is usually undertaken that a coating film is formed on the substrate surface with a composition sensitive to actinic rays such as ultraviolet light, X-rays, electron beams and the like, which is called a photoresist, followed by pattern-wise exposure of the coating film to the actinic rays and development to form a patterned photoresist layer.
Photoresist compositions are classified into positive-working and negative-working ones depending on the change in the solubility behavior by the exposure to actinic rays. Namely, the positive-working photoresist is imparted with increased solubility in a developing solution in the exposed areas and remains insoluble in the unexposed areas while the negative-working photoresist behaves inversely. Typical positive-working photoresist compositions currently on use include combinations of an alkali-soluble novolac resin as the base ingredient and a naphthoquinone diazide compound as a photosensitizer. While such a naphthoquinone diazide-based positive-working photoresist can be developed with an aqueous alkaline solution as the developing solution, aqueous alkaline solutions containing metal ions are undesirable as a developing solution in the manufacture of semiconductor devices because the metal ions may adversely influence the performance of the semiconductor devices processed by the development therewith. Accordingly, developing solutions containing no metal ions should be used in such a case as exemplified by an aqueous solution of tetramethyl ammonium hydroxide disclosed in IBM Technical Disclosure Bulletin, volume 13, No. 7, page 2009 (1970) and an aqueous solution of choline disclosed in U.S. Pat. No. 4,239,661.
One of the difficult problems in the patterning using a positive-working photoresist is the change in the sensitivity depending on the temperautre of the developing solution or the so-called temperature dependency of the developing solution. Namely, for example, the line width of a patterned photoresist layer is subject to variation depending on the temperature of the developing solution while it is a very difficult matter to exactly control the temperature of the developing solution in the procedures of stationary development and spraying development prevailingly practiced in recent years. Therefore, it is eagerly desired to develop a developing solution having a characteristic of outstandingly small temperature dependency in development.
The apparatuses of development currently used in the manufacture of integrated circuits are mostly and increasingly designed for performing stationary development in order to facilitate automatization of the photoresist processing. The stationary development is a process in which a developing solution is dripped to and spread over the surface of a semiconductor silicon wafer coated with a layer of a photoresist composition and, after standing as such for a while, the developing solution is again dripped so that the whole process of development proceeds with the wafer kept stationary throughout. In such a process of stationary development, the spreading velocity of the developing solution over the whole surface of the wafer is the key factor which is determinant of the uniformity of the line width in the patterned photoresist layer on the wafer surface. This problem of spreadability of the developing solution over the wafer surface is more important as the silicon wafers have a larger and larger diameter so that the wettability of the developing solution is one of the most important characteristics required of the solution.
In order to improve the wettability of a developing solution, a method is disclosed in Japanese Patent Kokai No. 58-57128 according to which the developing solution is admixed with 1 to 50% by weight of an organic solvent or a surface active agent. When a hydrophilic solvent such as alcohols, ethylene glycol monoalkyl ethers and the like is added to a developing solution for positive-working photoresist composition such as an aqueous solution of tetramethyl ammonium hydroxide, no improving effect can be obtained in the wettability of the solution when the amount of the added organic solvent is small while increase of the amount of the organic solvent may cause a problem in the selectivity that the photoresist layer is dissolved away by the developing solution not only in the exposed areas but also in the unexposed areas to give an undesired pattern of the photoresist layer. When a surface active agent is added to the developing solution in place of the organic solvents, the problem of the temperature dependency of the developing solution cannot be solved so that the sensitivity is enhanced as the temperature is increased along with an increase in the film thickness reduction in the unexposed areas of the photoresist layer.
Besides, one of the important characteristics required of a developing solution for positive-working photoresist compositions is the so-called dissolving selectivity that dissolution of the photoresist layer is complete in the exposed areas while the photoresist layer in the unexposed areas should be left intact by the developing solution with an as small as possible change in the film thickness by the development. According to the disclosure in Japanese Patent Kokai Nos. 58-9143 and 58-150949, improvements in this regard can be obtained by the addition of a surface active agent of a quaternary ammonium type or a quaternary ammonium salt, respectively. Further, Japanese Patent Kokai No. 60-12547 teaches that contrast of a positive-working photoresist composition can be increased when it is developed using a developing solution containing an alkali metal-containing basic compound and a fluorine-containing surface active agent in combination. This method, however, is far from industrial practicability in the manufacture of semiconductor-based integrated circuits because alkali metal compounds are detrimental to the performance of semiconductor devices in addition to the problem that patterned photoresist layers with reliability can hardly be obtained due to the increased temperature dependency in the power of the developing solution.